FRIDAY, Feb. 10 (HealthDay News) -- The size of a man's prostate gland may help doctors predict the severity of his prostate cancer, according to a new study.

Researchers from the Vanderbilt-Ingram Cancer Center in Nashville, Tenn., found smaller prostates that produce higher levels of prostate specific antigen (PSA) in the blood are more often linked to serious forms of prostate cancer that require aggressive treatment.

"There's nothing about size that would necessarily predict a bad outcome. What it's really about is the ratio of PSA to size, or PSA density, meaning that a small prostate that is making a lot of PSA is likely to be due to a bad tumor, whereas a large prostate making a lot of PSA is likely to be due to benign enlargement of the prostate (BPH)," said the study's senior author, Dr. Daniel Barocas, an assistant professor of urologic surgery, in a university news release.

The study's authors suggest the findings could help doctors determine the best course of treatment for patients with prostate cancer. For instance, low-risk patients with a small prostate might benefit from aggressive treatment.

In conducting the study, they analyzed about 1,250 cases of prostate cancer among men who had their prostate gland removed but were considered to be low-risk because their cancer was classified as low grade.

Within that group, the researchers zeroed in on patients whose risk was considered so low that they might have qualified for less aggressive treatment, including watching and waiting. The study found that in 31 percent of cases considered low-risk in pre-surgical analysis, the prostate cancer was upgraded to more serious once pathologists examined the tissue removed during surgery. The researchers found men with smaller prostates were more likely to be among this group.

The study was recently published in the Journal of Urology.

The researchers pointed out that the findings are significant since men with prostate cancer who are considered low-risk may receive less aggressive treatment or just be placed under observation.

"Our field suffers from this great confusion because in half of men you can find prostate cancer in microscopic amounts that may not be clinically significant and yet it's the second leading cause of cancer death among men," Barocas noted. "The more you look for it, the more you find it but that doesn't help us figure out who needs treatment and who doesn't."

The researchers cautioned that more accurate tests are still needed to determine which cancers are actually threatening to patients.

"The imaging for prostate cancer is relatively weak because the disease tends to be diffuse, rather than growing in what we think of as a tumor -- a spherical nodule. Prostate cancer tends to grow along the glands in a sort of flat pattern, so it's a little harder to detect. A better test, which we don't yet have, would reliably image or identify where in the prostate the tumor lies," Barocas added.